Electrically actuated variable pressure control system

ABSTRACT

An electrically-actuated variable pressure control system for use with flow-controlled liquid application systems. Direct acting solenoid valves are pulsed at varying frequencies and duty cycles 0000 change the resistance to flow encountered by the flow-controlled liquid application system. This pulsing solenoid valve technique preserves a high degree of accuracy and uniformity through a wide range of pressure control. This wide range of pressure control indirectly allows the flow-controlled liquid application system to operate over a wider range of flow control, yielding indirect benefits to performance and productivity. When the solenoid valves are attached to pressure-atomization spray nozzles, control over spray pattern and droplet size is further achieved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 60/688,259, filed Jun. 7, 2005.

BACKGROUND OF THE INVENTION

Spraying is a well-known method of applying a wide variety of bulkmaterials, primarily in liquid or a mixture of liquid and powder in afluid propellant medium. Such spray materials can be dispensed in aircurrents, under liquid pressure, by gravity flow, or with any othersuitable discharge means.

Spray application of hulk materials offers many potential advantages,including efficiency, uniformity of coverage and flexibility to adaptspraying equipment to various conditions unique to the objects beingsprayed and their particular environments.

However, a disadvantage with many spray systems relates to the drift ofspray particles and droplets away from their intended targets. Suchdrift is at best inefficient, as in the case of the overspray whichrepresents wasted spray material, and in more serious situations cancause damage to nearby property, environment and people.

The field of agricultural spraying includes pesticide application forcrop pest management and the application of fertilizer and growthregulators for nutrient management. The agricultural spraying industryis quite large, with pesticides alone currently accounting forapproximately $3,000,000,000 in estimated annual expenditures. However,the use of pesticides in agricultural. applications produces substantialbenefits in crop yields with an estimated annual savings ofapproximately $12,000,000,000 in crops which would otherwise be lost topests. The spray application of fertilizers and growth regulatorslikewise produces substantial benefits in crop yields and the like.

Notwithstanding the substantial advantages of agricultural sprayingapplications of pesticides and other spray materials, agriculturalspraying is generally a relatively inefficient process. Factors whichcontribute to such inefficiencies include the susceptibility of sprayedmaterials to wind drift, overspray and inaccurate placement on theintended target crop plants. Irregularities in terrain and nonuniformplantings also contribute to the inconsistent and inefficientapplication of agricultural spray materials. Moreover, variations inambient conditions such as wind, humidity levels and temperature tend toreduce the uniformity and efficiency with which spray materials areapplied to their intended crop targets.

In addition to the inefficiencies associated with misdirectedagricultural spray materials, overspray and spray drift can createsignificant problems if the materials are inadvertently applied toadjoining areas for which they were not intended. Such misapplication ofagricultural spray materials can result in crop damage, injury tolivestock, contamination of environmentally-sensitive areas andunnecessary human exposure to toxic materials.

The problems associated with the misapplication of agricultural spraymaterials are exacerbated by the use of larger spraying equipmentcovering wider swaths, high speed vehicles, air-blast spraying, and byaerial spraying. The inherent difficulties associated with large-scalespraying operations are balanced against the relative efficiencies whichare achieved by covering larger areas more rapidly with wide-swathspraying equipment.

The Heiniger et al. U.S. Pat. No. 5,348,226 discloses a spray boomsystem with automatic boom end height control which uses an ultrasonicheight control system for conforming the spray boom orientations totopography and slope of a zone being sprayed in order to increaseuniformity of coverage, Uniform spray nozzle height can be a significantfactor in achieving uniform spray material coverage.

Another important factor in spray material deposition control is thedroplet size spectrum of the liquid being sprayed. Spray droplet sizehas been shown to significantly affect both the efficacy of pesticidetreatments and the potential for off-target spray movement. Suchoff-target movement and deposition of spray is often called “spraydrift”. Insecticides, fungicides, growth regulators and post-emergenceherbicides are generally more effective when applied using relativelysmall droplets, which tend to provide greater penetration of plantcanopies and uniform coverage of foliar surfaces. Smaller spraydroplets, with shorter mechanical relaxation times, have the advantageof more closely following air currents into dense plant canopies forachieving greater penetration and more uniform coverage. Conversely,such droplet mobility associated with smaller droplet sizes canexacerbate problems associated with spray drift away from applicationsites. Generally speaking, larger droplets tend to fall more directlydue to their greater mass and are thus less susceptible to spray drift,evaporation, etc.

A common technique for controlling the application rate of spray liquidinvolves adjusting the spray liquid pressure, for example, with the useof a throttling valve in a main distribution line of a spray liquiddistribution system. However, altering the liquid pressure alsogenerally alters the droplet size, thus effecting the deposition and itssusceptibility to spray drift, evaporation, etc.

The Giles et al. U.S. Pat. No. 5,134,961 discloses an electricallyactuated variable flow control system wherein solenoid valves areactuated by square wave pulses, which can be varied in frequency andduty cycle for controlling volumetric flow through spray nozzles. Thevolumetric flow rate can thus be varied without changing droplet sizeand spray pattern since the liquid supply pressure can be maintainedconstant.

In addition to the aforementioned advantages of independentlyandselectively controlling the application rate and median droplet sizesetpoints, substantial advantages can be achieved by controlling spraydeposition with respect to field position of a spray vehicle, such as aground vehicle or an aircraft. Such position-responsive control can beimportant because spray zones in and around a field to be sprayed canrequire different treatment by a spray system, ranging from little or noapplication of spray materials (i.e., outside the boundary of a givensite) to a maximum application rate in heavily infested areas or regionsof poor fertility. The boundaries for such differential application ratespray zones can be irregular, with such irregularities increasing thedifficulty of manually altering spray system operating conditions by anon-board operator. Moreover, problems can arise due to operator reactiontimes when changed field conditions call for adjustments to the sprayconditions. For example, if an operator is alerted that he or she hascrossed a field boundary or property line and initiates a procedure foraltering spray application, most spray control systems have an inherentdelay which may cause overspray problems,

To address some of these problems, control systems and methodology haveheretofore been developed that respond to spray vehicle positions. Forexample, Ortlip U.S. Pat. No. 4,630,773 discloses a method and apparatusfor spraying fertilizer wherein a computerized control system includes afield map with digital information concerning various soil types. Thecontrol system disclosed therein dispenses fertilizer in accordance withthe optimum applications for the different soil conditions encounteredin a target field, The spray liquid application rate is automaticallyadjusted for vehicle speed. Sensors are disclosed for determiningmalfunctions of the application hardware. However, the applicationcontrol provided by the Ortlip apparatus occurs only along the directionof travel and not along the boom section. Moreover, the Ortlip apparatusdoes not provide for droplet size control, drift control or spraytransport modeling for spray liquid deposition prediction.

Recent improvements in the accuracy and effectiveness of the globalpositioning system (GPS) for civilian applications have also createdopportunities for greater automation of agricultural spraying bycontrolling agricultural spraying equipment with positioning systemsresponsive to specific field conditions. For example, Teach U.S. Pat.No. 5,334,987 discloses an agricultural aircraft control system usingthe global positioning system. The Teach agricultural aircraft controlsystem is adapted for automatically opening a dispenser valve forreleasing chemicals in response to the aircraft flying within theboundaries of an agricultural field. Moreover, the Teach system providesfor recording flight data. However, the Teach system does not providefor droplet size control, drift reduction, spray transport modeling andgradients of application rates to avoid drift in the combination of thepresent invention.

Models for predicting dispersion and deposition of aerially releasedmaterial have been in development for approximately the past 35 years injoint projects between the U.S.D.A. Forest Service, in cooperation withthe U.S. Army. Computerized codes which are currently available includeAGDISP (Agricultural DISPersal) (Bilanin et al., 1989) and FSCBG (ForestService Cramer-Barry-Graham) (Teske et al., 1992b). Such computerizedmodels can be useful for predicting dispersion patterns of variousliquids under a variety of ambient conditions, heights, etc.

Giles et al. teach a “Networked Diagnostic and Control System forDispensing Apparatus”, U.S. patent application Ser. No. 11/135,054,filed May 23, 2005, which is incorporated herein by reference thereto,Giles et al, discloses monitoring the flow rate of a fluid through anozzle and monitoring the flow pattern that is emitted from the nozzle.A further need exists in the industry for a system that is also capableof maintaining a desired pressure in the system.

BRIEF SUMMARY OF THE INVENTION

In general, the present invention is directed to a system and method ofcontrolling pressure and flow for application of an agrochemical from anagricultural spraying system. The invention is suitable for use with anyof various types of spraying systems and in various and many applicationsystems, For example, the system of the present invention can be used inconjunction with agricultural spray systems that are designed to applyliquids to a field.

The component parts of the system are simple and economical tomanufacture, assemble and use. Other advantages of the invention will beapparent from the following description and the attached drawings, orcan be learned through practice of the invention.

In one embodiment of the present invention, an agricultural sprayingsystem includes a valve having a nozzle and an actuator assembly, thenozzle having an orifice defined therethrough, the actuator assemblybeing configured to control an emission of an agrochemical from theorifice; a pipe connected to the valve and configured to deliver theagrochemical thereto; a pressure sensor connected to the pipe forsensing a pressure in the pipe; and a pressure controller incommunication with the pressure sensor, the pressure controller beingconfigured to change a flow resistance based on the sensed pressure tomaintain a predetermined pressure in the pipe for the emission of theagrochemical from the orifice.

In this aspect of the invention, the nozzle is a pressure-atomizationspray nozzle is configured to produce a desired droplet size spectra andan agrochemical spray pattern.

Also in this aspect of the invention, the actuator assembly includes areciprocating solenoid actuator configured to move relative to theorifice when a voltage is applied to the reciprocating solenoidactuator.

Further in this aspect of the invention, the actuator assembly includesa coil, a guide, and a plunger, the coil being disposed about the guide,the plunger being interposed between the guide and the orifice and beingconfigured to move relative to the orifice when a voltage is applied tothe coil.

In this aspect of the invention, the agricultural spraying systemfurther includes means for controlling the actuator assembly, theactuator assembly defining an open position and a closed position. Themeans for controlling can be a square wave generator being configured toapply a voltage to the actuator assembly to move the actuator assemblyfrom the closed position to the open position for the emission of theagrochemical from the orifice.

Also in this aspect of the invention, the square wave generator isconfigured to modulate a square wave frequency and a duty cycle tochange the flow resistance for the emission of the agrochemical from theorifice. The square wave generator can be located in or in communicationwith the pressure controller.

Further in this aspect of the invention, the agricultural sprayingsystem includes an agrochemical tank for holding the agrochemical, theagrochemical tank connected to the pipe.

In this aspect of the invention, the agricultural spraying system canalso have a pump for pumping the agrochemical through the pipe. The pumpcan be a positive displacement pump or a centrifugal pump.

Also in this aspect of the invention, the agricultural spraying systemcan have a wheel and a piston, the piston connected to the wheel and tothe positive displacement pump, the piston being configured toreciprocate the positive displacement pump as the wheel turns.

Further in this aspect of the invention, the agricultural sprayingsystem includes a plurality of valves, each of the valves beingconfigured for independent operation, or at least two of the valvesbeing configured as a group to stop the emission of the agrochemicalfrom the group.

In another embodiment of the present invention, an agricultural sprayingsystem includes an actuating valve including a nozzle and an actuatorassembly, the nozzle having an orifice defined therethrough, theactuator assembly being configured to control an emission of anagrochemical from the orifice; a pipe connected to the actuating valveand configured to deliver the agrochemical thereto; a regulating valveconnected to the pipe for regulating a predetermined flow rate of theagrochemical through the pipe; a flow controller in communication withthe regulating valve to control the predetermined flow rate; a pressuresensor connected to the pipe for sensing a pressure in the pipe and apressure controller in communication with the pressure sensor, thepressure controller being configured to change a flow resistance basedon the sensed pressure to maintain a predetermined pressure in the pipefor the emission of the agrochemical from the orifice, the predeterminedpressure dictated by the flow resistance.

In this aspect of the invention, the agricultural spraying systemfurther includes a square wave generator being configured to apply avoltage to the actuator assembly to move the actuator assembly from aclosed position to an open position for the emission of the agrochemicalfrom the orifice. More particularly, the square wave generator canmodulate a square wave frequency and a duty cycle to change the flowresistance for the emission of the agrochemical from the orifice.

Also in this aspect of the invention, the pressure controller determinesthe predetermined flow resistance based on a system speed, a systemcondition, an application rate, a target area size, a geographiclocation, a field position, a weather phenomenon and combinationsthereof.

Further in this aspect of the invention, the pressure controllerdetermines the predetermined pressure and maintains the predeterminedpressure based on a system speed, a system condition, an applicationrate, a target area size, a geographic location, a field position, aweather phenomenon and combinations thereof.

In this aspect of the invention, the agricultural spraying system alsoincludes a controller configured to set the predetermined resistance toflow.

In yet another embodiment of the present invention, a method ofcontrolling pressure and flow for application of an agrothemical from anagricultural spraying system is provided. The method includes pumping anagrochemical from a tank through a pipe to an actuating valve includinga nozzle and an actuator assembly, the nozzle having an orifice definedtherethrough, the actuator assembly being configured to control anemission of the agrochemical from the orifice; regulating apredetermined flow rate of the agrochemical through the pipe by aregulating valve connected to the pipe; controlling the predeterminedflow rate with a flow controller in communication with the regulatingvalve; sensing a pressure in the pipe using a pressure sensor connectedto the pipe; and changing a flow resistance with a pressure controllerbased on the sensed pressure to maintain a predetermined pressure in thepipe, the pressure controller in communication with the pressure sensor,the pressure controller being configured to for the emission of theagrochemical from the orifice, the predetermined pressure dictated bythe flow resistance.

In this aspect of the invention, the method further includes changingthe flow rate to change the pressure.

Also in this aspect of the invention, the method further includesassessing correctness of the flow rate with the flow controller.

Further in this aspect of the invention, the method includes opening theregulating valve when the flow rate is too low.

Also in this aspect of the invention, the method further includesclosing the regulating valve when the flow rate is too high.

In this aspect of the invention, the method further includes assessingcorrectness of the sensed pressure with the pressure sensor.

Also in this aspect of the invention, the method further includesincreasing flow resistance when the sensed pressure is too low.

In this aspect of the invention, decreasing a duty cycle of a squarewave increases flow resistance.

Further in this aspect of the invention, the method includes decreasingflow resistance when the sensed pressure is too high.

In this aspect of the invention, increasing a duty cycle of a squarewave decreases flow resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects and advantages of the invention will be apparent fromthe following description, or can be learned through practice of theinvention, in combination with the drawings, which serve to explain theprinciples of the invention but by no means are intended to beexhaustive of all of possible manifestations of the invention. Thus, atleast one embodiment of the invention is shown in the drawings in which:

FIG. 1 is a perspective view of a dispensing system according to anaspect of the present invention installed in an environment for which itis intended to be used;

FIG. 2 is a schematic of a flow control system that can be employed inthe system of FIG. 1, particularly showing a ground-speed-compensating,positive-displacement pump and an electrically-actuated variablepressure control system according to one aspect of the invention;

FIG. 3A shows a sectional view of a solenoid valve in an open position;

FIG. 3B shows a sectional view of the solenoid valve as in FIG. 3A in aclosed position;

FIG. 4 shows a puke width modulation technique for various duty cyclesemployed in the electrically-actuated pressure control system as in FIG.1;

FIG. 5 is a schematic of another flow control system that can beemployed in the system of FIG. 1, particularly showing a flow meter, aflow regulating valve and an electrically-actuated variable pressurecontrol system;

FIG. 6 is a graph showing an interdependent relationship between flowcontrol and pressure control when an electrically-actuated variablepressure control system is used in conjunction with a flow controlsystem according to an aspect of the invention;

FIG. 7 shows a flow chart of control logic employed by the flow controlsystem and the pressure control system as in FIG. 6; and

FIG. 8 is an elevational view of a control panel used to control theforegoing embodiments according to a further aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Detailed reference will now be made to the drawings in which examplesembodying the present invention are shown. The detailed description usesnumerical and letter designations to refer to features of the drawings.Like or similar designations of the drawings and description have beenused to refer like or similar parts of the invention.

The drawings and detailed description provide a full and writtendescription of the invention, and of the manner and process of makingand using it, so as to enable one skilled in the pertinent art to makeand use it, as well as the best mode of carrying out the invention.However, the examples set forth in the drawings and detailed descriptionare provided by way of explanation only and are not meant as limitationsof the invention, The present invention thus includes any modificationsand variations of the following examples as come within the scope of theappended claims and their equivalents.

As broadly embodied in FIGS. 1 and 2, an exemplary agricultural. system,designated in general by the numeral 10, broadly includes a tractor 12having an electrically-actuated variable pressure control system 14. Asshown, the tractor 12 includes a cab 16, a plurality of wheels 18A atleast one boom wheel 18B for engaging a section of ground with a crop,produce, product or the like (generally, P), a tank or reservoir 22, anda spray boom 24 with a plurality of nozzles 34 attached to the sprayboom 24. The tank 22 holds a liquid, a mixture of liquid and powder, orother product designated in general by the letter S. The liquid can be aquantity of water or an agrochemical such as a fertilizer or apesticide. Likewise, the liquid-powder mixture can be the agrochemical.Thus, the product S can be sprayed from the nozzles 34 onto a crop orproduct or the ground. P itself as shown in FIG. 1 and described ingreater detail by example operation below.

FIG. 2 more particularly shows the boom wheel 18B attached to aslider-crank or piston mechanism 26, which is connected to a groundspeed compensating positive displacement pump 28. As shown, the boomwheel 18B rolls across the ground P and turns a slider-crank mechanism26, which reciprocates the positive displacement pump 28. The positivedisplacement pump 28 is calibrated to apply a specific amount per acreof product S to soil of the ground P.

As briefly introduced, the product S is contained in the tank 22 andenters the positive displacement pump 28 through a suction pipe 30. Theproduct S flows from the positive displacement pump 28, through a boompipe 32, to the direct acting solenoid valve equipped nozzles 34, Asshown in FIGS. 1 and 2, the product S flows from the nozzles 34 and isapplied to the ground P in various ways; e.g., pulsed, patterned and thelike as taught by Giles et al, in U.S. Pat. No. 5,134,961 andincorporated herein by reference thereto. The skilled artisan willappreciate that pipe as used herein can mean any type of conduit or tubemade of any suitable material such as metal or plastic. The skilledartisan will further appreciate that other ground application devicescan be added to provide varying effects of placement of the products ontop or below a soil surface of the ground F, such as via pipes, knives,coulters, and the like.

FIG. 2 further shows a pressure sensor 52, which measures the pressurein the boom pipe 32. The pressure sensor 52 sends this pressureinformation to a pressure controller 54. In this example, the pressurecontroller 54 pulses the direct acting solenoid valve equipped nozzles34 with a frequency and duty cycle that maintains a specific pressurewithin the boom pipe 32. An example of this operation is describedbelow.

Turning now to FIGS. 3A and 3B, the direct acting solenoid valveequipped nozzle 34 is shown respectively in open and closed positions.The direct acting solenoid nozzle 34 pulses with a frequency and dutycycle such that an orifice 40 is active only when the valve-equippednozzle 34 is open. The frequency is sufficiently fast to diminish anyeffects of pulsing on the total system, therefore creating a controlledvariable resistance to flow.

More specifically, as shown in FIGS. 3A and 3B, the nozzle 34 has a body36 including mounting means such as a bracket or screw-fitting 38 formounting the nozzle 34 to the boom pipe 32. As shown, the orifice 40 isconfigured for outlet flow F1 and inlet flow F2. This aspect of theinvention is described in greater detail below.

As particularly shown in FIG. 3B, the nozzle 34 also includes anactuator assembly 41, which has an actuator or coil 42 located on oraround a guide 44. As shown, a plunger 46 is movably positioned betweenthe guide 44 and the orifice 40. A square wave generator 55 is connectedto the nozzle 34 and applies an electric signal or voltage 56 to thecoil 42, which establishes a magnetic field. The magnetic field causesthe guide 44 to become magnetized, which attracts the plunger 46. Inthis example, the magnetic force of the guide 44 overcomes a springforce of a spring 48 and a force of the inlet flow F2 as applied to theorifice 40. When the plunger 46 lifts a seal 50 from the orifice 40, theoutlet flow F1 results.

FIG. 4 shows a pulse width modulation (PWM) signal used to actuate thedirect acting solenoid nozzle 34 as in FIGS. 1 and 2. In this example,the electric signal 56 is pulsed with a fixed period length 58 of 0.1seconds. When the signal 56 is high; i.e., when voltage is present, thepulse is shown at the ON position. As shown, the signal 56 remains highor ON for a portion of the period length 58 before switching low; i.e.,no voltage is present. The relation of on-time to period length 58 iscalled a duty cycle 60 and is measured in percent (%). Three duty cyclesof 30%, 50% and 90% are shown in FIG. 4. As described with respect toFIG. 3 above, the directing acting solenoid nozzle 34 will open andclose with this on/off pulse. For example, if the duty cycle 60 is 50%,the resulting resistance to flow will be 50% of the total resistance toflow of the orifice 40. Similar respective results occur with the 30%and 90% duty cycles 60.

Turning now to FIG. 5, an agricultural spraying system 110 includes anelectrically-actuated flow control system 114 including a flow meter 162and a flow regulating valve 172. Many of the components of theagricultural spraying system 110 are similar to the components of theforegoing embodiments as described above and reference is made theretofor an enabling description of these components if not expresslydescribed below.

As in the previously described embodiment, a product S in FIG. 5 flowsfrom a tank 122 to a centrifugal pump 128 via a suction pipe 130. Asshown, the product S flows from the centrifugal pump 128 to the flowregulating valve 172 via a pressure pipe 170. The flow regulated productS flows to the flow meter 162, to a pressure sensor 152, and to thedirect acting solenoid valve equipped nozzles 134 via a boom pipe 132.Thus, the product S is delivered to a target such as the crop or groundP in FIG. 1 via spray atomization nozzles 151 of the direct actingsolenoid valves 134.

More particularly, the flow meter 162 in FIG. 5 measures the flow rateand sends a signal to a flow controller 164. The flow controller 164receives target rate information from a rate input device 168 and speedfrom a speed input device 166. Accordingly, the flow controller 164controls the flow regulating valve 172 to the desired rate.Additionally, the pressure sensor 152 measures the pressure in the boompipe 132 and sends the pressure information to a pressure controller154. The pressure controller 154 pulses the direct acting solenoid valveequipped nozzles 134 with a frequency and duty cycle which maintains aspecific pressure within the pipe 132.

The skilled artisan will appreciate that a conventional flow-controlsystem operates by shifting a flow control system curve along a fixedpressure control curve. The intersection of the two curves is theresultant conventional application flow and pressure. As the flowchanges in such a conventional system, the intersection changesaccordingly such that a new system pressure is achieved as a directresult of the flow change.

FIG. 6 generally shows an interdependent relationship between flowcontrol and pressure control when an electrically-actuated variablepressure control system is used in conjunction with a flow controlsystem. More specifically, FIG. 6 shows a relative, pressure-versus-flowrelationship for liquid flow-control systems, and anelectrically-actuated variable pressure control system as describedabove.

As shown in FIG. 6, an electrically-actuated pressure control systemaccording to the present invention allows a pressure control curve 190to be shifted in various directions indicated by a double-headed arrow194, which is an independent shift from a change in a flow indicated bya double-headed arrow 192. The result is that an intersection 196 may benavigated to any flow and pressure setting desired by an operator,within limits of the system. This ability, when controlled by flow andpressure controllers, allows the operator to set flow and pressure setpoints independently, and have both set points maintained throughout arange of speed. In addition, the flow set point may be changed withouteffecting the pressure set point, and vise versa.

With reference now to FIGS. 5, 6 and 7, a control logic is employed bythe flow controller 164 and the electrically-actuated variable pressurecontrol system 154 according to an aspect of the invention. Inparticular, FIG. 7 shows start-up of the flow control system 164 at stepA. A flow is read at step B, and a calculation occurs to determine ifthe flow is too high or too low. This calculation may be simple orcomplex depending on the variables upon which flow is being controlled.As shown at step C, if the flow is too low, a restriction is relieved byopening the flow regulating valve 172 as in FIG. 5. Conversely, if theflow is too high at step D, a restriction can be increased by closingthe flow regulating valve 172. The routine of reading and changing flowis operated continuously while the flow-control system 164 is active.Those skilled in the art will appreciate that alternate mechanisms andmethods of changing flow may be employed; for instance, by using theground driven positive pump 28 of FIG. 1, or by changing the speed ofthe pump 28.

Also shown in FIG. 7, the control logic of the electrically-actuatedvariable pressure control system 154 is similar to that of the flowcontrol system 164 described above. Upon start-up of the pressurecontrol system 154 at step F, a duty cycle is initiated at step C at adesired value, which is 50% in this example. This value can be set at acontrol panel 174 as described below with respect to FIG. 8. Theinitiated value is held for a predetermined or initiation time (step H)while the flow control system 164 adjusts to the target flow. When theinitiation time is over, the pressure is read at step I. If the pressureis too low, the resistance to flow is increased at step J by decreasingthe duty cycle 60 of the direct acting solenoid nozzle 134. Conversely,if the pressure is too high, the resistance to flow is decreased at stepK by increasing the duty cycle 60 of the direct acting solenoid nozzle134, When the pressure control system 154 is stopped, the initializingduty cycle is reset to the last known duty cycle. This delay allows theflow control system 164 to initialize and grants some priority to flowover pressure.

FIG. 8 shows an embodiment of the control panel 174, briefly introducedabove, for the electrically-actuated pressure control system 154. Thecontrol panel 174 is mounted in a vehicle such as in the cab 16 of thetractor 12 at FIG. 1 within reach of the operator. In this example, aknob 176 is shown having twelve detents 180. These twelve detents 180indicate a target pressure set point, or duty cycle, that the controller154/164 is to maintain.

As shown in FIG. 8, a mode of operation is dictated by a switch 182. Inthis example, the three position switch 182 is off in a center position,in a “PSI” mode in an uppermost position, and in a “PWM %” mode in adownward position. Thus, the position of the switch 182 in FIG. 8indicates whether the knob 176 detent is calibrated for PSI or PWM %.Making two modes of operation available reduces down-time in the eventof a system failure. For instance, in PWM % mode, the system can be runfrom manually calculated settings until the automatic pressure controlsystem can be repaired,

As further shown in FIG. 8, a color graphic 178 can be utilized to guidethe operator to more advantageous settings of the knob 176. Forinstance, desirable ranges can be color coded green, less desirableranges can be yellow and ranges that should be used sparingly or avoidedcan be colored orange or red.

Also shown in FIG. 8, a connector 184 is attached to a wiring harness,which connects the panel 174 to other components of the system 110. Oneskilled in the art will appreciate how the connector 184 connects thepanel 174 and further description is not necessary to understand andpractice this aspect of the invention.

These and other modifications and variations to the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may he interchanged either in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention.

1-29. (canceled)
 30. An agricultural spraying system comprising: a valveincluding a nozzle and an actuator assembly, the nozzle having anorifice defined therethrough, the actuator assembly configured to becontinuously pulsed according to a duty cycle to control emission of anagrochemical from the orifice; a pipe connected to the valve andconfigured to deliver the agrochemical to the valve; a pressure sensorconnected to the pipe for sensing a pressure in the pipe; and a pressurecontroller in communication with the pressure sensor, the pressurecontroller configured to: compare the sensed pressure to a pressure setpoint; and change a flow resistance through the orifice based on thecomparison by adjusting the duty cycle of the actuator assembly tomaintain the pressure in the pipe at the pressure set point.
 31. Theagricultural spraying system of claim 30, wherein the agriculturalspraying system further comprises a control panel configured to receivea user input, wherein the pressure controller is further configured todetermine the pressure set point based on the user input.
 32. Theagricultural spraying system of claim 31, wherein the user input is thepressure set point.
 33. The agricultural spraying system of claim 30,wherein the pressure set point is a single pressure value.
 34. Theagricultural spraying system of claim 30, wherein the actuator assemblyis continuously pulsed at a frequency of 10 Hz.
 35. The agriculturalspraying system of claim 30, wherein the nozzle is apressure-atomization spray nozzle configured to produce a desireddroplet size spectra and an agrochemical spray pattern.
 36. Theagricultural spraying system of claim 30, wherein the actuator assemblyincludes a reciprocating solenoid actuator configured to move relativeto the orifice when a voltage is applied to the reciprocating solenoidactuator.
 37. The agricultural spraying system of claim 30, wherein theactuator assembly includes a coil, a guide, and a plunger, wherein thecoil is disposed about the guide, and wherein the plunger is interposedbetween the guide and the orifice and moves relative to the orifice whena voltage is applied to the coil.
 38. The agricultural spraying systemof claim 30 further comprising a plurality of valves, each valve of theplurality of valves including a nozzle and an actuator assembly, whereinthe pressure controller adjusts the duty cycle of the actuator assemblyof each valve independently of the other valves of the plurality ofvalves.
 39. The agricultural spraying system of claim 30, wherein thepressure controller changes the flow resistance by adjusting the dutycycle of the actuator assembly to one of a plurality of duty cycles, theplurality of duty cycles including a maximum duty cycle, a minimumcycle, and at least one duty cycle between the maximum duty cycle andthe minimum duty cycle.
 40. The agricultural spraying system of claim30, wherein the minimum duty cycle is 30% and the maximum duty cycle is90%.
 41. The agricultural spraying system of claim 30, wherein theactuator assembly is movable between an open position, in which theagrochemical is permitted to flow through the orifice, and a closedposition, in which the actuator assembly seals the orifice.
 42. Theagricultural spraying system of claim 41, further comprising anactuating signal generator for controlling actuation of the actuatorassembly between the open position and the closed position.
 43. Theagricultural spraying system of claim 42, wherein the actuating signalgenerator is a square wave generator configured to actuate the actuatorassembly from the closed position to the open position by applying avoltage to the actuator assembly.
 44. The agricultural spraying systemof claim 43, wherein the square wave generator is configured to modulatea square wave frequency and the duty cycle to change the flow resistancefor the emission of the agrochemical from the orifice.
 45. Theagricultural spraying system of claim 44, wherein the pressurecontroller includes the square wave generator.
 46. The agriculturalspraying system of claim 30, wherein the pressure controller changes theflow resistance through the orifice by increasing the duty cycle atwhich the actuator assembly is pulsed to decrease the flow resistancewhen the sensed pressure exceeds the pressure set point.
 47. Theagricultural spraying system of claim 30, wherein the pressurecontroller changes the flow resistance through the orifice by decreasingthe duty cycle at which the actuator assembly is pulsed to increase theflow resistance when the sensed pressure is less than the pressure setpoint.
 48. The agricultural spraying system of claim 30 furthercomprising an agrochemical tank for holding the agrochemical, theagrochemical tank connected to the pipe.
 49. The agricultural sprayingsystem of claim 30 further comprising a pump for pumping theagrochemical through the pipe.
 50. The agricultural spraying system ofclaim 49, wherein the pump is one of a positive displacement pump and acentrifugal pump.
 51. The agricultural spraying system of claim 49,wherein the pump is a positive displacement pump, the agriculturalspraying system further comprising a wheel and a piston, wherein thepiston is connected to the wheel and to the positive displacement pump,and wherein the piston is configured to reciprocate the positivedisplacement pump as the wheel turns.
 52. A method for regulatingpressure for application of an agrochemical from an agriculturalspraying system, the method comprising: directing the agrochemicalthrough a pipe of the agricultural spraying system to an actuating valveincluding a nozzle and an actuator assembly, the nozzle having anorifice defined therethrough; continuously pulsing the actuator assemblyaccording to a duty cycle to control emission of the agrochemical fromthe orifice; sensing a pressure in the pipe using a pressure sensorconnected to the pipe; comparing, using a pressure controller, thesensed pressure to a pressure set point; and changing a flow resistancethrough the orifice, using the pressure controller, based on thecomparison by adjusting the duty cycle of the actuator assembly tomaintain the pressure in the pipe at the pressure set point.
 53. Themethod of claim 52 further comprising: receiving a user input at acontrol panel; and determining, using the pressure controller, thepressure set point based on the user input.
 54. The method of claim 53,wherein the user input is the pressure set point.
 55. The method ofclaim 52, wherein changing a flow resistance through the orificeincludes transmitting control signals from the pressure controller tothe actuator assembly, the control signals being associated with theduty cycle.
 56. The method of claim 55, wherein the control signals aregenerated by a square wave generator associated with the pressurecontroller.
 57. The method of claim 52, wherein changing a flowresistance through the orifice includes increasing the duty cycle atwhich the actuator assembly is pulsed in order to decrease the flowresistance when the sensed pressure exceeds the pressure set point. 58.The method of claim 52, wherein changing a flow resistance through theorifice includes decreasing the duty cycle at which the actuatorassembly is pulsed in order to increase the flow resistance when thesensed pressure is less than the pressure set point.
 59. The method ofclaim 52, wherein the actuator assembly is continuously pulsed such thatthe pressure in the pipe is maintained at the pressure set pointindependently of a predetermined flow rate of the agrochemical throughthe pipe.
 60. The method of claim 59, further comprising regulating thepredetermined flow rate of the agrochemical through the pipe using aregulating valve connected to the pipe.
 61. The method of claim 52,wherein the actuator assembly is movable between an open position, inwhich the agrochemical is permitted to flow through the orifice, and aclosed position, in which the actuator assembly seals the orifice. 62.The method of claim 52, wherein the pressure set point is a singlepressure value.
 63. A pressure controller for use with an agriculturalspraying system including a valve including a nozzle and an actuatorassembly, the nozzle having an orifice defined therethrough, theactuator assembly configured to be continuously pulsed according to aduty cycle to control emission of an agrochemical from the orifice, apipe connected to the valve and configured to deliver the agrochemicalto the valve, and a pressure sensor connected to the pipe for sensing apressure in the pipe, wherein the pressure controller is configured to:receive a sensed pressure in the pipe from the pressure sensor; comparethe sensed pressure in the pipe to a pressure set point; and change aflow resistance through the nozzle orifice based on the comparison byadjusting the duty cycle of the actuator assembly to maintain thepressure in the pipe at the pressure set point.